The present invention relates to a two-dimensional image detector in which a sensitive semiconductor layer converts optical information or radiological information corresponding to a two-dimensional image of a detection subject to electrical charge information; an active matrix substrate reads the electrical charge information; and an amplifying electric. circuit portion amplifies the electrical charge information, so that the electrical charge information is converted into an electrical signal for an image. More specifically, the present invention relates to a technology for preventing a disturbance from entering the electrical signal when the amplifying electric circuit portion converts the electrical charge information into the electrical signal for an image.
An X-ray apparatus used in a medical institution such as a hospital is provided with a flat-panel radiation detector (hereinafter abbreviated to “FPD”) as a two-dimensional image detector for detecting a transmission X-ray image (two-dimensional image) of a subject (not shown) when X-ray is irradiated on the subject. The FPD has two types, i.e., a direct conversion type in which X-ray is directly converted into electrical charge, and an indirect conversion type in which X-ray is converted into light, and light is converted into electrical charge.
As shown in FIG. 10, the direct conversion type of the FPD includes a sensitive semiconductor layer 51 for converting X-ray information corresponding to a transmission X-ray image of a detection subject into electrical charge information; and an active matrix substrate 52 for retrieving the electrical charge information converted on the sensitive semiconductor layer 51. The sensitive semiconductor layer 51 is formed on the active matrix substrate 52. An electrode 53 is laminated on the sensitive semiconductor layer 51 for applying a bias voltage. When the transmission X-ray image is detected, the transmission X-ray image projected on the sensitive semiconductor layer 51 is converted into the electrical charge on the sensitive semiconductor layer 51, and retrieved on the active matrix substrate 52. Then, the transmission X-ray image projected on the sensitive semiconductor layer 51 is amplified in an amplifying electric circuit portion 54, and converted into an electrical signal for an X-ray picture (for example, refer to Patent Reference 1).
Instead of the electrode 53 for applying a bias voltage, the indirect conversion type of the FPD includes a photoelectric converting layer (not shown) formed on the sensitive semiconductor layer for converting the X-ray information corresponding to the transmission X-ray image of the detection subject into optical information, as well as the sensitive semiconductor layer. The indirect conversion type of the FPD has a structure essentially same as that of the direct conversion type of the FPD, except that the sensitive semiconductor layer converts light converted by the photoelectric converting layer into the electrical charge. Patent Reference 1; Japanese Patent Publication (Kokai) No. 2001-320035
In the direct conversion type and the indirect conversion type of the FPDs, a disturbance tends to enter when the electrical charge information is converted into the electrical signal for an X-ray picture on the amplifying electric circuit portion 54.
An amount of information of the electrical charge (quantity of electrical charge) is extremely small, so that the amplifying electric circuit portion 54 needs to amplify the electrical charge information with a high gain (high amplification rate). In the amplifying electric circuit portion 54 with a high gain, a disturbance is amplified with a high gain along with the electrical charge information. Accordingly, a disturbance inevitably enters when the electrical charge information is converted into the electrical signal. When the disturbance enters the electrical signal for an X-ray picture, a final X-ray picture may have deteriorated quality. Accordingly, it is necessary to prevent a disturbance from entering when the electrical charge information is converted into the electrical signal.
In view of the problems mentioned above, an object of the present invention is to provide a two-dimensional image detector capable of blocking a disturbance when an amplifying electric circuit portion converts electrical charge information into an electrical signal for an image after optical information or radiological information corresponding to a two-dimensional image of a detection subject is converted into the electrical charge information.
Further objects and advantages of the invention will be apparent from the following description of the invention.